Direct and Indirect Effects of Full-Sib Recurrent Selection for Resistance to Common Rust (Puccinia sorghi Schw.) in Three Sweet Corn Populations

Common rust (Puccinia sorghi Schw.) is a major pathogen of sweet corn (Zea mays L.). Recurrent selection may be useful for improving resistance to common rust. The objectives of this study were to (i) evaluate three sweet corn populations (Minn11, Minn14, NECDR) after three cycles of full-sib recurrent selection for resistance to common rust evaluated 40 d after pollination (DAP), (ii) determine if selection increased resistance 21 DAP, and (iii) determine if selection affected agronomic traits related to plant architecture, maturity, and yield. Cycles 0 to 3 from each population were evaluated under artificial rust infestation in 1989, 1990, 1993, 1994, and 1995, and without infestation in 1994 and 1995. Percent leaf area infected declined linearly from 37.0 to 8.2% in Minn11 (R² = 0.98) and 57.0 to 9.9% in NECDR (R² = 0.98) evaluated 40 DAP, and from 22.5 to 7.8% in Minn11 (R² = 0.89) and from 22.8 to 10.0% in NECDR (R² = 0.91) evaluated 21 DAP. Population Minn14 tended to have decreased percent leaf area infected over cycles, but the response was not significant because of cycle × year interactions in each experiment. Most agronomic traits decreased linearly over cycles except for ear weight/stover weight ratio in Minn11 and NECDR, and silk delay in Minn14, which increased linearly. In general, plants tended to be more compact and flower earlier over cycles. Selection for plant type, ear weight, and flowering time should accompany selection for resistance to common rust. Research supported by Hatch Funds allocated to the Wisconsin Agric. Exp. Stn., the College of Agric. and Life Sci., the Graduate School, Univ. of Wisconsin-Madison, the Univ. of Wisconsin Pioneer Hi-Bred Plant Breeding Fellowship awarded to B.G. Abedon, and The Midwest Food Processors Association. Submitted by the senior author as partial fulfillment of the Ph.D. degree.